Impacts of climate change on wheat anthesis and fusarium ear blight in the UK

Climate change will affect both growth of agricultural crops and diseases that attack them but there has been little work to study how its impacts on crop growth influence impacts on disease epidemics. This paper investigates how impacts of climate change on wheat anthesis date will influence impacts on fusarium ear blight in UK mainland arable areas. A wheat growth model was used for projections of anthesis dates, and a weather-based model was developed for use in projections of incidence of fusarium ear blight in the UK. Daily weather data, generated for 14 sites in arable areas of the UK for a baseline (1960–1990) scenario and for high and low CO₂ emissions in the 2020s and 2050s, were used to project wheat anthesis dates and fusarium ear blight incidence for each site for each climate change scenario. Incidence of fusarium ear blight was related to rainfall during anthesis and temperature during the preceding 6 weeks. It was projected that, with climate change, wheat anthesis dates will be earlier and fusarium ear blight epidemics will be more severe, especially in southern England, by the 2050s. These projections, made by combining crop and disease models for different climate change scenarios, suggest that improved control of fusarium ear blight should be a high priority in industry and government strategies for adaptation to climate change to ensure food security.     

Geographic variation in severity of phoma stem canker and <Emphasis Type="Italic">Leptosphaeria maculans/ L. biglobosa</Emphasis> populations on UK winter oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis>)

Phoma stem canker, caused by Leptosphaeria maculans and L. biglobosa, is the most important disease of oilseed rape in Europe. Differences between L. maculans and L. biglobosa in their life-cycles enable the two species to co-exist on oilseed rape crops over a cropping season. This review considers the factors affecting geographic variation in the severity of phoma stem canker epidemics and in the structure of the population of the pathogens in the UK, where the most severe epidemics occur in the south of England and cankers do not develop in Scotland. It is concluded that this variation is directly related to differences in climate, since weather-based models show that stem canker severity increases with increasing winter/spring temperature and temperatures are greater in the south of the UK. It may also be related to differences in pathogen populations, since surveys showed that the proportion of the more damaging L. maculans in stem cankers was greatest in southern England, with most L. biglobosa in northern England. Regional variation in agronomic practices such as cultivar choice and fungicide use may also indirectly influence phoma stem canker severity. Differences in cultivar choice result in differences in L. maculans race structure, which may influence the severity of epidemics. Differences in fungicide use may also influence pathogen populations, since L. maculans and L. biglobosa differ in their sensitivities to different azole fungicides. These factors are discussed in relation to strategies for sustainable production of oilseed rape by adaptation to threats posed by climate change.     

Overview on the review articles published during the past 30 years relating to the potential climate change effects on plant pathogens and crop disease risks

From 1988 to July 2019 more than 100 review articles were published, including opinion papers and book chapters, that focused on potential climate change effects on plant pathogens and the future crop disease risks. Therefore, an overview of them is presented herein, particularly helpful for beginners and non-experts in climate change biology research. Specifically, this overview contributes to a faster and more convenient identification of appropriate review articles, for example, related to a certain crop, pathogen, plant disease or country of interest. However, not all important crops, pathogens, diseases and countries are considered specifically and in-depth in any of these review articles, suggesting that there are still research gaps prevalent, which are also highlighted herein. Nevertheless, the overview suggests that researchers are increasingly busy and successful in summarizing the fragmented information spread throughout the international literature. Consequently, they are providing ‘step-by-step’ a comprehensive, in-depth, and continuously updated knowledge platform on potential climate change effects on plant pathogens and the respective crop disease risks in the future, although some aspects will, by nature, be repeated.     

Climate change and potential future risks through wheat diseases: a review

This review summarizes the most significant results from the so far existing, but fragmented studies on the potential effects of climate change on wheat pathogens and the diseases they cause. The analysis demonstrates that predictions are uncertain and future disease risk trends must be differentiated on a geographic and time scale. For example, disease incidence of Fusarium head blight in the United Kingdom might increase middle of this century, whereas disease severity of Septoria tritici blotch might decrease in France end of this century. Thus, wheat disease problems caused by a changing climate will probably not consistently worsen, as climatic changes may also improve the crop health situation in wheat depending on the location. The results of long-term simulations of future disease risk must be taken with caution, because different climate models and downscaling methods are used to make the projections and this can create considerable uncertainty. Being aware of this short-coming, plant pathologists recently started to assess the sources of uncertainty related to their long-term disease simulations. However, in spite of this progress there is still a significant lack of simulation studies related to different wheat diseases in various locations that could help to estimate future wheat grain losses due to climatic changes. Many more of these studies are certainly needed. Otherwise, the focus in the climate change debate will remain on the yield loss/gain potential due to changes in the environmental conditions only, which would neglect the important impact of altered biotic constraints such as diseases which are among the key factors in the estimation of future global wheat productivity.     

Climate change impacts on plant canopy architecture: implications for pest and pathogen management

Climate change influences on pests and pathogens are mainly plant-mediated. Rising carbon dioxide and temperature and altered precipitation modifies plant growth and development with concomitant changes in canopy architecture, size, density, microclimate and the quantity of susceptible tissue. The modified host physiology and canopy microclimate at elevated carbon dioxide influences production, dispersal and survival of pathogen inoculum and feeding behaviour of insect pests. Elevated temperature accelerates plant growth and developmental rates to modify canopy architecture and pest and pathogen development. Altered precipitation affects canopy architecture through either drought or flooding stress with corresponding effects on pests and pathogens. But canopy-level interactions are largely ignored in epidemiology models used to project climate change impacts. Nevertheless, models based on rules of plant morphogenesis have been used to explore pest and pathogen dynamics and their trophic interactions under elevated carbon dioxide. The prospect of modifying canopy architecture for pest and disease management has also been raised. We offer a conceptual framework incorporating canopy characteristics in the traditional disease triangle concept to advance understanding of host-pathogen-environment interactions and explore how climate change may influence these interactions. From a review of recent literature we summarize interrelationships between canopy architecture of cultivated crops, pest and pathogen biology and climate change under four areas of research: (a) relationships between canopy architecture, microclimate and host-pathogen interaction; (b) effect of climate change related variables on canopy architecture; (c) development of pests and pathogens in modified canopy under climate change; and (d) pests and pathogen management under climate change.     

Evaluation of models to predict take-all incidence in winter wheat as a function of cropping practices,soil, and climate

The incidence and severity of take-all, caused by Gaeumannomyces graminis var. tritici (Ggt), in susceptible crops depend on climate, soil characteristics and cropping practices. Take-all can be controlled by modifying crop rotation, crop management and fungicide treatment. When available, fungicides are used as a seed treatment and are partially effective. There is currently no reliable method for helping farmers to optimise their choice of cropping system to improve take-all control. In this study, we defined 16 models, based on various mathematical functions and input variables, for predicting disease incidence in a wheat crop as a function of soil characteristics, climate, crop rotation and crop management. The parameters of these models were estimated from field experiments carried out at six sites in the north of France over a ten-year period. The root mean squared error of prediction (RMSEP) values of the models were estimated by cross validation and compared. RMSEP was in the range 16.34–65.93% and was higher for the models based on multiplicative functions. The lowest RMSEP value was obtained for a dynamic model simulating disease incidence during the crop cycle and which included among input variables the percentage of diseased plants determined at GS30.     

Simulation modelling of yield losses caused by wheat stem rust

Stem rust, or black rust, of wheat, caused by Puccinia graminis f. sp. tritici, has recently re-emerged in several parts of the world, with epidemics occurring in eastern Africa, as well as northern and southern Europe. Damage mechanisms from disease dynamically affect the physiology of the crop as it grows and develops, and as the epidemic progresses, leading to yield losses in the stem rust-diseased wheat stand. Process-based agrophysiological models that include disease-induced damage mechanisms can help to better understand the physiological processes leading to yield losses, and to inform strategic decisions such as breeding strategies. Such models have not been developed for wheat stem rust so far. Two damage mechanisms for stem rust, light stealing and assimilate diversion, were incorporated in the agrophysiological simulation model WHEATPEST. The model, tested from experimental field data retrieved from the literature, provides a satisfactory representation of the system, although consistently underestimates relative yield losses by about 6.9%, resulting in relative yield losses between 17% and 56%. Analyses highlight the importance of the diversion of assimilates toward the pathogen in the magnitude of yield loss. Considering only the reduction of green leaf area would underestimate damage from stem rust by at least threefold. The analysis also shows the importance of the dynamic interplay between disease and crop growth, especially the dynamics of leaf area, on yield loss. Directions to consider additional damage mechanisms are proposed, and perspectives for future research, especially in relation to plant breeding strategies under climate change, are offered.     

The impact of global warming on plant diseases and insect vectors in Sweden

Cold winters and geographic isolation have hitherto protected the Nordic countries from many plant pathogens and insect pests, leading to a comparatively low input of pesticides. The changing climate is projected to lead to a greater rise in temperature in this region, compared to the global mean. In Scandinavia, a milder and more humid climate implies extended growing seasons and possibilities to introduce new crops, but also opportunities for crop pests and pathogens to thrive in the absence of long cold periods. Increased temperatures, changed precipitation patterns and new cultivation practices may lead to a dramatic change in crop health. Examples of diseases and insect pest problems predicted to increase in incidence and severity due to global warming are discussed.     

Disease-weather relationships for powdery mildew and yellow rust on winter wheat

Key weather factors determining the occurrence and severity of powdery mildew and yellow rust epidemics on winter wheat were identified. Empirical models were formulated to qualitatively predict a damaging epidemic (>5% severity) and quantitatively predict the disease severity given a damaging epidemic occurred. The disease data used was from field experiments at 12 locations in the UK covering the period from 1994 to 2002 with matching data from weather stations within a 5 km range. Wind in December to February was the most influential factor for a damaging epidemic of powdery mildew. Disease severity was best identified by a model with temperature, humidity, and rain in April to June. For yellow rust, the temperature in February to June was the most influential factor for a damaging epidemic as well as for disease severity. The qualitative models identified favorable circumstances for damaging epidemics, but damaging epidemics did not always occur in such circumstances, probably due to other factors such as the availability of initial inoculum and cultivar resistance.     

Control of crop diseases through Integrated Crop Management to deliver climate-smart farming systems for low- and high-input crop production

Crop diseases affect crop yield and quality and cause significant losses of total food production worldwide. With the ever-increasing world population and decreasing land and water resources, there is a need not only to produce more food but also to reduce agricultural greenhouse gas (GHG) emissions to mitigate climate change and avoid land use change and biodiversity loss. Thus, alternative climate-smart farming systems need to adapt to produce more food per hectare in a more sustainable way than conventional high-input farming systems. In addition to breeding new high-yielding cultivars adapted to future climates, there is a need to deploy Integrated Crop Management (ICM) strategies, relying less on synthetic inputs for fertilization and crop protection and less on fossil fuel-powered machinery to decrease yield losses due to pest and pathogens and guarantee food security. In this review, we compare some low-input farming systems to conventional agricultural systems with a focus on ICM solutions being developed to reduce synthetic inputs; these include crop genetic resistance to pathogens, intercropping, canopy architecture manipulation, and crop rotation. These techniques have potential to decrease crop disease frequency and severity by decreasing amounts and dispersal of pathogen inoculum and by producing microclimates that are less favourable for pathogen development, while decreasing GHG emissions and improving environmental sustainability. More research is needed to determine the best deployment of these ICM strategies in various cropping systems to maximize yield, crop protection, and other ecosystem services to address trade-offs between climate change and food security.     

植物真菌和卵菌病暴发的起源和传播

传染病暴发在植物、动物和人群中很常见。除了少数已发展为流行病和大流行病外,在很大程度上大多数传染病暴发的原因仍未知,植物真菌和卵菌病暴发尤其如此。所有流行病和大流行病都是从局部暴发开始,然后蔓延到更广泛的地理区域,因此了解其初始暴发的原因对于有效预防和控制植物病害流行病和大流行病至关重要。该文首先描述疾病暴发的定义和检测,随后简要描述导致植物传染病暴发的主要原因,包括寄主植物、病原体及其相关的环境因素,以一种真菌和一种卵菌病原体为例简要概述宿主病原体系统,并强调分子工具在帮助揭示病原体的起源和传播及其暴发及大流行方面的作用。由于人为活动及气候的加速变化,植物病害暴发的可能性越来越大,最后提出应该如何应对其暴发。     

Ecological Genomics and Epidemiology

The huge amount of genomic data now becoming available offers both opportunities and challenges for epidemiologists. In this “preview” of likely developments as the field of ecological genomics evolves and merges with epidemiology, we discuss how epidemiology can use new information about genetic sequences and gene expression to form predictions about epidemic features and outcomes and for understanding host resistance and pathogen evolution. DNA sequencing is now complete for some hosts and several pathogens. Microarrays make it possible to measure gene expression simultaneously for thousands of genes. These tools will contribute to plant disease epidemiology by providing information about which resistance or pathogenicity genes are present in individuals and populations, what genes other than those directly involved in resistance and virulence are important in epidemics, the role of the phenotypic status of hosts and pathogens, and the role of the status of the environmental metagenome. Conversely, models of group dynamics supplied by population biology and ecology may be used to interpret gene expression within individual organisms and in populations of organisms. Genomic tools have great potential for improving understanding of resistance gene evolution and the durability of resistance. For example, DNA sequence analysis can be used to evaluate whether an arms race model of co-evolution is supported. Finally, new genomic tools will make it possible to consider the landscape ecology of epidemics in terms of host resistance both as determined by genotype and as expressed in host phenotypes in response to the biotic and abiotic environment. Host phenotype mixtures can be modeled and evaluated, with epidemiological predictions based on phenotypic characteristics such as physiological age and status in terms of induced systemic resistance or systemic acquired resistance.     

Wheat diseases on the prairies: A Canadian story

Canada is one of the largest wheat producers in the world, and wheat is grown over an area spanning most of the southern latitudes, with the prairie region (provinces of Saskatchewan, Alberta, and Manitoba) being the main producer. Several pathogens and pests attack wheat, but at present fusarium head blight (FHB), stripe rust, and leaf spots are the most damaging diseases to wheat production in Canada. Historically, smuts, stem rust, and leaf rust caused major crop losses in Canada and can still pose serious threat if management practices are relaxed. Cropping practices used by Canadian farmers to grow and harvest wheat over the last century have influenced disease development and pathogen biology, affecting the severity, incidence, and prevalence of crop diseases over time. Changes such as reduced tillage coincide with emergence of residue-borne diseases, such as FHB and leaf spots, while the deployment of resistant cultivars and increased fungicide use has resulted in the reduction of common bunt, stem, and leaf rust. This review will discuss the influence of long-term cropping practices, alone or in combination, on the biology, emergence, and prevalence of wheat diseases in Canada over the last century.     

Genetic control of partial resistance to ‘collar’ and ‘root’ isolates of <Emphasis Type="Italic">Phoma macdonaldii</Emphasis> in sunflower

Phoma macdonaldii is one of the most important pathogens of sunflower (Heliantus annuus) in France. In order to determine the inheritance of resistance to the disease, five sunflower genotypes with wide genetic variability for resistance to two ‘collar’ and two ‘root’ Phoma isolates were crossed in a diallel programme. Four separate experiments were undertaken under controlled conditions. In each one, the response of parental genotypes and their F1 hybrids were evaluated with one of the four Phoma isolates. Analysis of variance was performed to determine the effects of genotype on disease severity score when inoculated with ‘collar’ or ‘root’ Phoma isolates and showed significant variability among parents and F1 hybrids for disease severity score. Diallel analysis showed that general combining ability (GCA) and specific combining ability (SCA) effects for resistance to ‘collar’ and ‘root’ Phoma isolates were highly significant for each of the four isolates indicating that both kinds of gene effects were important in controlling the resistance. The GCA/SCA ratios were more than one for three out of four isolates showing that additive genetic effects were more important than non-additive effects for resistance to three of the studied Phoma isolates. Hence, conventional breeding methods could be recommended to achieve genetic improvement to such ‘collar’ and ‘root’ Phoma isolates.     

Effect of crop growth and canopy filtration on the dynamics of plant disease epidemics spread by aerially dispersed spores

Most mathematical models of plant disease epidemics ignore the growth and phenology of the host crop. Unfortunately, reports of disease development are often not accompanied by a simultaneous and commensurate evaluation of crop development. However, the time scale for increases in the leaf area of field crops is comparable to the time scale of epidemics. This simultaneous development of host and pathogen has many ramifications on the resulting plant disease epidemic. First, there is a simple dilution effect resulting from the introduction of new healthy leaf area with time. Often, measurements of disease levels are made pro rata (per unit of host leaf area or total root length or mass). Thus, host growth will reduce the apparent infection rate. A second, related effect, has to do with the so-called "correction factor," which accounts for inoculum falling on already infected tissue. This factor accounts for multiple infection and is given by the fraction of the host tissue that is susceptible to disease. As an epidemic develops, less and less tissue is open to infection and the initial exponential growth slows. Crop growth delays the impact of this limiting effect and, therefore, tends to increase the rate of disease progress. A third and often neglected effect arises when an increase in the density of susceptible host tissue results in a corresponding increase in the basic reproduction ratio, R(0), defined as the ratio of the total number of daughter lesions produced to the number of original mother lesions. This occurs when the transport efficiency of inoculum from infected to susceptible host is strongly dependent on the spatial density of plant tissue. Thus, crop growth may have a major impact on the development of plant disease epidemics occurring during the vegetative phase of crop growth. The effects that these crop growth-related factors have on plant disease epidemics spread by airborne spores are evaluated using mathematical models and their importance is discussed. In particular, plant disease epidemics initiated by the introduction of inoculum during this stage of development are shown to be relatively insensitive to the time at which inoculum is introduced.     

Rational arrangement of a network for disease survey on a regional scale*

The forecasting and warning system of Emilia‐Romagna region (Italy) produces warnings for crop protection against diseases, using information from weather stations, biological surveys on a network of observation fields and simulation models. The network of field observations is crucial for the efficiency of the service but, unfortunately, the human and economic resources available for their management are usually less than needed. Therefore, the number of observation fields is insufficient to cover the entire territory uniformly, so that their geographical distribution increases in importance. In this work, a method for rational arrangement of observation fields on a regional scale is proposed. It uses models simulating crop growth and disease outbreak, both using meteorological data available on a 5‐km mesh, to draw maps showing homogeneous areas within the territory. For the main pathogens of winter wheat (Erysiphe graminis, Puccinia striiformis, Puccinia recondita and Fusarium subsp.), disease risk is calculated when host plants are susceptible to infection, and both static and dynamic maps are drawn. The use of maps is discussed in arranging observation fields and in timing field surveys.     

In‐field molecular diagnosis of plant pathogens: recent trends and future perspectives

Accurate management practices in crop health and food safety are critical, especially regarding the detection of plant pathogens in the early stages of a disease. To date, specific, fast and sensitive technologies for point‐of‐care diagnosis and simple or grower‐friendly devices are very valuable, as no specialized staff are required for diagnosing a disease in the field. This is especially the case today, when factors such as climate change may cause the appearance of pathogens in areas where years ago they were unexpected. The aim of this research is to review some of the promising techniques that can be applied to in‐field molecular detection of plant pathogens and how these techniques can change the way farmers and pathologists are diagnosing plant diseases. Some of them, like loop‐mediated isothermal amplification and recombinase polymerase amplification, are already being successfully used for routine diagnosis. However, most technologies still need validation in the plant pathology field, where they have a promising future for in‐field diagnosis when combined with simple DNA extraction methods, reagent stabilization techniques and their integration into portable devices.     

The effect of powdery mildew (Erysiphe graminis f. sp. hordei) and leaf rust (Puccinia hordei) on spring barley in New Zealand. II. Apical development and yield potential

Reduced yields caused by powdery mildew and leaf rust in two seasons were associated with reduced plant growth. Combinations of early, late and full epidemics in one season, and 12 epidemic combinations in the second, were designed to identify crop sensitivity to disease by comparing growth and development with healthy plants. Early epidemics reduced ear number by increasing tiller death, and reduced grain number by effects on spikelet, floret or grain abortion, depending on the type of epidemic. Epidemics later in crop growth increased floret and grain abortion and also reduced grain weight.
There was no compensation by later-determined components for reduced growth and delayed development at earlier growth stages. Plants infected at early growth stages were more sensitive to late infections, seen as effects on the later-determined components, than plants which were healthy initially. Interactions occurred between epidemics at different times and are likely to occur between diseases and other constraints.     

Effect of light duration and growth season on verticillium wilt in potato

The tolerance response to Verticillium in potato is affected by external abiotic and biotic factors. Short-day photoperiod enhanced disease level in the susceptible cvs. ‘Nicola’ and ‘Maris Bard’, as well as in the tolerant cvs. ‘Cara’ and ‘Désirée‘. This was observed under field conditions, where plant reaction in the spring was compared with that in autumn. In some cases the disease was more pronounced in autumn, with its shorter days, than in spring, when the days are longer. The effect was measured by disease symptom severity, fungus colonization in the plants, plant height and final yield. This disease enhancement was more pronounced under controlled growth room conditions, where the only different parameter was illumination. A short photoperiod of 8 h increased the disease level relative to 16 h of light.     

Gesunde Pflanzen unter zukünftigem Klima

Predicted changes in average values of global climate variables (increased temperatures, altered precipitation patterns, increased concentrations of atmospheric CO₂) and changes in the frequency, duration, and degree of extremes (frost, heat, drought, hail, storms, floods, etc.) will affect agricultural crops, agroecosystems, and agricultural productivity. Although forecasts of regional climate changes are still imprecise, mean temperature increases in Europe are expected to be greater in the north (2.5–4.5°C) than in the south (1.5–4.5°C). Regional forecasts for precipitation changes are also very far from precise; however, problems with drought are expected to increase, especially in Mediterranean countries. Overall, shortage of water will be the predominant factor affecting plant growth. As higher temperatures are known to enhance plant development and especially the grain-filling duration of cereals, grain yield losses are possible in a warmer climate. On the other hand, elevated atmospheric CO₂ concentrations are known to stimulate photosynthesis and enhance growth and yield (“CO₂ fertilization”); concomitantly, leaf transpiration is reduced, resulting in improved water use efficiency. Total biomass and yield were enhanced by 20–30% in experiments with elevated CO₂ exposure (550–700 ppm) under more or less ideal growth conditions. Elucidating the interactions between positive and negative effects of climate change is of crucial importance for any prediction of future crop yields. The present paper is a brief summary mainly of the potential effects of elevated temperatures and atmospheric CO₂ on crop growth, quality, and yield. Also, adaptation measures, possible interactive effects of different climate variables, and interactions of climate change components with other growth variables (pathogens, air pollutants) are briefly described.